线程安全性（一） 原子性 基于锁的实现 - 基于synchronized实现的计数器

基于synchronized实现的计数器

• 用AtomicInteger可以实现对计数器的原子性操作；
• 把计数器的操作放在用synchronized修饰的方法中同样可以实现对计数器的原子性操作；

import com.example.concurrency.annotations.ThreadSafe;
import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;

@Slf4j
@ThreadSafe
public class CountExample3 {

    // 请求总数
    public static int clientTotal = 5000;

    // 同时并发执行的线程数
    public static int threadTotal = 200;

    public static int count = 0;

    public static void main(String[] args) throws Exception {
        ExecutorService executorService = Executors.newCachedThreadPool();
        final Semaphore semaphore = new Semaphore(threadTotal);
        final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
        for (int i = 0; i < clientTotal ; i++) {
            executorService.execute(() -> {
                try {
                    semaphore.acquire();
                    add();
                    semaphore.release();
                } catch (Exception e) {
                    log.error("exception", e);
                }
                countDownLatch.countDown();
            });
        }
        countDownLatch.await();
        executorService.shutdown();
        log.info("count:{}", count);
    }

    private synchronized static void add() {
        count++;
    }

}

输出：

18:25:17.423 [main] INFO com.example.concurrency.example.count.CountExample3 - count:5000